1. Field of the Invention
The present invention relates to an evaluating method, and more particularly to a method for evaluating efficacy of prevention maintenance for a tool.
2. Description of Related Art
For manufacturing equipments, prevention maintenances (PM) for tools are very important works. Good prevention maintenance time arrangements can improve productivity and yield of the whole manufacturing equipments and the availability of the tools. On the contrary, an improper prevention maintenance time arrangement not only reduces productivity and yield, but also causes tool failure.
For equipments with high manufacturing costs and precision equipments, prevention maintenances are more important. For example, in semiconductor processes, when wafers are lapped by a lapping tool, recourse costs of basic consumables are wasted if the prevention maintenances are executed too early. Because it takes at least two or three hours, even one day, to execute one prevention maintenance, so the usage rate of the lapping tool decreases, and further the productivity decreases. On the contrary, if the prevention maintenances are executed too late, the demand of size precision of products cannot be achieved, which reduces the yield of the whole products and even causes the failure of the whole lapping tool.
At present, most of semiconductor manufacturers do the prevention maintenances for semiconductor tools regularly, that is, semiconductor tools are maintained preventively at fixed intervals. After semiconductor tools are maintained preventively, it is believed that the semiconductor tools are adjusted to be in a good state, manufacturing capacities of the semiconductor tools meet the demands and the yield of wafer production is improved.
However, in fact, it cannot ensure that prevention maintenances of semiconductor tools are helpful to wafer production. It is possible that wafers processed by the semiconductor tools which have just been preventively maintained, still have reduced yield.
Accordingly, how to evaluate correctly efficacy of prevention maintenances on wafer production is a problem to be solved.
Hence, the inventors of the present invention believe that the shortcomings described above are able to be improved and finally suggest the present invention which is of a reasonable design and is an effective improvement based on deep research and thought.